Camera filters are never designed to be one-size-fits-all. Nevertheless, this shouldn't stop you from using one that's lying around, just because it does not fit your DSLR lens.
Samuel Chapman is one such photographer who found that he was stuck with a great camera that could not accommodate his neutral density filters.
Determined to use them, he devised a ‘makeshift’ adaptor which was made out of a sponge, which he affectionately named, ‘FX Sponge Filter Holder 5000.’
If you're uncomfortable with the idea of a yellowish sponge at the end of your camera - you can always dye the sponge black.
Here's a comparison to show that the FX Sponge Filter Holder 5000 really works at holding a filter in place:
Details on how Chapman's sponge looked like on his camera and how it fitted a filter, below:
[via Petapixel.com]